bug 13460: suggestion.tt now uses Price plugin

bug 13460: suggestion.tt now uses Price plugin

To test:

1/ Add a new suggestion, put some values for the price
2/ View the suggestion in the staff interface
2/ Switch the currency format
3/ Notice the format of the price does not change
4/ Apply patch
5/ Notice now the syspref is respected

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Works as described, thx!

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
(cherry picked from commit df2e9169b23ad3ecfbbf73367a19cb9117fb4ed4)
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>